Merging upstream version 1.71.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1087 insertions, 0 deletions

diff --git a/vendor/syn-1.0.109/src/punctuated.rs b/vendor/syn-1.0.109/src/punctuated.rs
new file mode 100644
index 000000000..b7d0185e8
--- /dev/null
+++ b/vendor/syn-1.0.109/src/punctuated.rs
@@ -0,0 +1,1087 @@
+//! A punctuated sequence of syntax tree nodes separated by punctuation.
+//!
+//! Lots of things in Rust are punctuated sequences.
+//!
+//! - The fields of a struct are `Punctuated<Field, Token![,]>`.
+//! - The segments of a path are `Punctuated<PathSegment, Token![::]>`.
+//! - The bounds on a generic parameter are `Punctuated<TypeParamBound,
+//!   Token![+]>`.
+//! - The arguments to a function call are `Punctuated<Expr, Token![,]>`.
+//!
+//! This module provides a common representation for these punctuated sequences
+//! in the form of the [`Punctuated<T, P>`] type. We store a vector of pairs of
+//! syntax tree node + punctuation, where every node in the sequence is followed
+//! by punctuation except for possibly the final one.
+//!
+//! [`Punctuated<T, P>`]: Punctuated
+//!
+//! ```text
+//! a_function_call(arg1, arg2, arg3);
+//!                 ~~~~^ ~~~~^ ~~~~
+//! ```
+
+#[cfg(feature = "extra-traits")]
+use std::fmt::{self, Debug};
+#[cfg(feature = "extra-traits")]
+use std::hash::{Hash, Hasher};
+#[cfg(any(feature = "full", feature = "derive"))]
+use std::iter;
+use std::iter::FromIterator;
+use std::ops::{Index, IndexMut};
+use std::option;
+use std::slice;
+use std::vec;
+
+use crate::drops::{NoDrop, TrivialDrop};
+#[cfg(feature = "parsing")]
+use crate::parse::{Parse, ParseStream, Result};
+#[cfg(feature = "parsing")]
+use crate::token::Token;
+
+/// A punctuated sequence of syntax tree nodes of type `T` separated by
+/// punctuation of type `P`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Punctuated<T, P> {
+    inner: Vec<(T, P)>,
+    last: Option<Box<T>>,
+}
+
+impl<T, P> Punctuated<T, P> {
+    /// Creates an empty punctuated sequence.
+    #[cfg(not(syn_no_const_vec_new))]
+    pub const fn new() -> Self {
+        Punctuated {
+            inner: Vec::new(),
+            last: None,
+        }
+    }
+
+    /// Creates an empty punctuated sequence.
+    #[cfg(syn_no_const_vec_new)]
+    pub fn new() -> Self {
+        Punctuated {
+            inner: Vec::new(),
+            last: None,
+        }
+    }
+
+    /// Determines whether this punctuated sequence is empty, meaning it
+    /// contains no syntax tree nodes or punctuation.
+    pub fn is_empty(&self) -> bool {
+        self.inner.len() == 0 && self.last.is_none()
+    }
+
+    /// Returns the number of syntax tree nodes in this punctuated sequence.
+    ///
+    /// This is the number of nodes of type `T`, not counting the punctuation of
+    /// type `P`.
+    pub fn len(&self) -> usize {
+        self.inner.len() + if self.last.is_some() { 1 } else { 0 }
+    }
+
+    /// Borrows the first element in this sequence.
+    pub fn first(&self) -> Option<&T> {
+        self.iter().next()
+    }
+
+    /// Mutably borrows the first element in this sequence.
+    pub fn first_mut(&mut self) -> Option<&mut T> {
+        self.iter_mut().next()
+    }
+
+    /// Borrows the last element in this sequence.
+    pub fn last(&self) -> Option<&T> {
+        self.iter().next_back()
+    }
+
+    /// Mutably borrows the last element in this sequence.
+    pub fn last_mut(&mut self) -> Option<&mut T> {
+        self.iter_mut().next_back()
+    }
+
+    /// Returns an iterator over borrowed syntax tree nodes of type `&T`.
+    pub fn iter(&self) -> Iter<T> {
+        Iter {
+            inner: Box::new(NoDrop::new(PrivateIter {
+                inner: self.inner.iter(),
+                last: self.last.as_ref().map(Box::as_ref).into_iter(),
+            })),
+        }
+    }
+
+    /// Returns an iterator over mutably borrowed syntax tree nodes of type
+    /// `&mut T`.
+    pub fn iter_mut(&mut self) -> IterMut<T> {
+        IterMut {
+            inner: Box::new(NoDrop::new(PrivateIterMut {
+                inner: self.inner.iter_mut(),
+                last: self.last.as_mut().map(Box::as_mut).into_iter(),
+            })),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as borrowed
+    /// punctuated pairs.
+    pub fn pairs(&self) -> Pairs<T, P> {
+        Pairs {
+            inner: self.inner.iter(),
+            last: self.last.as_ref().map(Box::as_ref).into_iter(),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as mutably
+    /// borrowed punctuated pairs.
+    pub fn pairs_mut(&mut self) -> PairsMut<T, P> {
+        PairsMut {
+            inner: self.inner.iter_mut(),
+            last: self.last.as_mut().map(Box::as_mut).into_iter(),
+        }
+    }
+
+    /// Returns an iterator over the contents of this sequence as owned
+    /// punctuated pairs.
+    pub fn into_pairs(self) -> IntoPairs<T, P> {
+        IntoPairs {
+            inner: self.inner.into_iter(),
+            last: self.last.map(|t| *t).into_iter(),
+        }
+    }
+
+    /// Appends a syntax tree node onto the end of this punctuated sequence. The
+    /// sequence must previously have a trailing punctuation.
+    ///
+    /// Use [`push`] instead if the punctuated sequence may or may not already
+    /// have trailing punctuation.
+    ///
+    /// [`push`]: Punctuated::push
+    ///
+    /// # Panics
+    ///
+    /// Panics if the sequence does not already have a trailing punctuation when
+    /// this method is called.
+    pub fn push_value(&mut self, value: T) {
+        assert!(
+            self.empty_or_trailing(),
+            "Punctuated::push_value: cannot push value if Punctuated is missing trailing punctuation",
+        );
+
+        self.last = Some(Box::new(value));
+    }
+
+    /// Appends a trailing punctuation onto the end of this punctuated sequence.
+    /// The sequence must be non-empty and must not already have trailing
+    /// punctuation.
+    ///
+    /// # Panics
+    ///
+    /// Panics if the sequence is empty or already has a trailing punctuation.
+    pub fn push_punct(&mut self, punctuation: P) {
+        assert!(
+            self.last.is_some(),
+            "Punctuated::push_punct: cannot push punctuation if Punctuated is empty or already has trailing punctuation",
+        );
+
+        let last = self.last.take().unwrap();
+        self.inner.push((*last, punctuation));
+    }
+
+    /// Removes the last punctuated pair from this sequence, or `None` if the
+    /// sequence is empty.
+    pub fn pop(&mut self) -> Option<Pair<T, P>> {
+        if self.last.is_some() {
+            self.last.take().map(|t| Pair::End(*t))
+        } else {
+            self.inner.pop().map(|(t, p)| Pair::Punctuated(t, p))
+        }
+    }
+
+    /// Determines whether this punctuated sequence ends with a trailing
+    /// punctuation.
+    pub fn trailing_punct(&self) -> bool {
+        self.last.is_none() && !self.is_empty()
+    }
+
+    /// Returns true if either this `Punctuated` is empty, or it has a trailing
+    /// punctuation.
+    ///
+    /// Equivalent to `punctuated.is_empty() || punctuated.trailing_punct()`.
+    pub fn empty_or_trailing(&self) -> bool {
+        self.last.is_none()
+    }
+
+    /// Appends a syntax tree node onto the end of this punctuated sequence.
+    ///
+    /// If there is not a trailing punctuation in this sequence when this method
+    /// is called, the default value of punctuation type `P` is inserted before
+    /// the given value of type `T`.
+    pub fn push(&mut self, value: T)
+    where
+        P: Default,
+    {
+        if !self.empty_or_trailing() {
+            self.push_punct(Default::default());
+        }
+        self.push_value(value);
+    }
+
+    /// Inserts an element at position `index`.
+    ///
+    /// # Panics
+    ///
+    /// Panics if `index` is greater than the number of elements previously in
+    /// this punctuated sequence.
+    pub fn insert(&mut self, index: usize, value: T)
+    where
+        P: Default,
+    {
+        assert!(
+            index <= self.len(),
+            "Punctuated::insert: index out of range",
+        );
+
+        if index == self.len() {
+            self.push(value);
+        } else {
+            self.inner.insert(index, (value, Default::default()));
+        }
+    }
+
+    /// Clears the sequence of all values and punctuation, making it empty.
+    pub fn clear(&mut self) {
+        self.inner.clear();
+        self.last = None;
+    }
+
+    /// Parses zero or more occurrences of `T` separated by punctuation of type
+    /// `P`, with optional trailing punctuation.
+    ///
+    /// Parsing continues until the end of this parse stream. The entire content
+    /// of this parse stream must consist of `T` and `P`.
+    ///
+    /// *This function is available only if Syn is built with the `"parsing"`
+    /// feature.*
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse_terminated(input: ParseStream) -> Result<Self>
+    where
+        T: Parse,
+        P: Parse,
+    {
+        Self::parse_terminated_with(input, T::parse)
+    }
+
+    /// Parses zero or more occurrences of `T` using the given parse function,
+    /// separated by punctuation of type `P`, with optional trailing
+    /// punctuation.
+    ///
+    /// Like [`parse_terminated`], the entire content of this stream is expected
+    /// to be parsed.
+    ///
+    /// [`parse_terminated`]: Punctuated::parse_terminated
+    ///
+    /// *This function is available only if Syn is built with the `"parsing"`
+    /// feature.*
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse_terminated_with(
+        input: ParseStream,
+        parser: fn(ParseStream) -> Result<T>,
+    ) -> Result<Self>
+    where
+        P: Parse,
+    {
+        let mut punctuated = Punctuated::new();
+
+        loop {
+            if input.is_empty() {
+                break;
+            }
+            let value = parser(input)?;
+            punctuated.push_value(value);
+            if input.is_empty() {
+                break;
+            }
+            let punct = input.parse()?;
+            punctuated.push_punct(punct);
+        }
+
+        Ok(punctuated)
+    }
+
+    /// Parses one or more occurrences of `T` separated by punctuation of type
+    /// `P`, not accepting trailing punctuation.
+    ///
+    /// Parsing continues as long as punctuation `P` is present at the head of
+    /// the stream. This method returns upon parsing a `T` and observing that it
+    /// is not followed by a `P`, even if there are remaining tokens in the
+    /// stream.
+    ///
+    /// *This function is available only if Syn is built with the `"parsing"`
+    /// feature.*
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse_separated_nonempty(input: ParseStream) -> Result<Self>
+    where
+        T: Parse,
+        P: Token + Parse,
+    {
+        Self::parse_separated_nonempty_with(input, T::parse)
+    }
+
+    /// Parses one or more occurrences of `T` using the given parse function,
+    /// separated by punctuation of type `P`, not accepting trailing
+    /// punctuation.
+    ///
+    /// Like [`parse_separated_nonempty`], may complete early without parsing
+    /// the entire content of this stream.
+    ///
+    /// [`parse_separated_nonempty`]: Punctuated::parse_separated_nonempty
+    ///
+    /// *This function is available only if Syn is built with the `"parsing"`
+    /// feature.*
+    #[cfg(feature = "parsing")]
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "parsing")))]
+    pub fn parse_separated_nonempty_with(
+        input: ParseStream,
+        parser: fn(ParseStream) -> Result<T>,
+    ) -> Result<Self>
+    where
+        P: Token + Parse,
+    {
+        let mut punctuated = Punctuated::new();
+
+        loop {
+            let value = parser(input)?;
+            punctuated.push_value(value);
+            if !P::peek(input.cursor()) {
+                break;
+            }
+            let punct = input.parse()?;
+            punctuated.push_punct(punct);
+        }
+
+        Ok(punctuated)
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Clone for Punctuated<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        Punctuated {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+impl<T, P> Eq for Punctuated<T, P>
+where
+    T: Eq,
+    P: Eq,
+{
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+impl<T, P> PartialEq for Punctuated<T, P>
+where
+    T: PartialEq,
+    P: PartialEq,
+{
+    fn eq(&self, other: &Self) -> bool {
+        let Punctuated { inner, last } = self;
+        *inner == other.inner && *last == other.last
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+impl<T, P> Hash for Punctuated<T, P>
+where
+    T: Hash,
+    P: Hash,
+{
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        let Punctuated { inner, last } = self;
+        inner.hash(state);
+        last.hash(state);
+    }
+}
+
+#[cfg(feature = "extra-traits")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "extra-traits")))]
+impl<T: Debug, P: Debug> Debug for Punctuated<T, P> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let mut list = f.debug_list();
+        for (t, p) in &self.inner {
+            list.entry(t);
+            list.entry(p);
+        }
+        if let Some(last) = &self.last {
+            list.entry(last);
+        }
+        list.finish()
+    }
+}
+
+impl<T, P> FromIterator<T> for Punctuated<T, P>
+where
+    P: Default,
+{
+    fn from_iter<I: IntoIterator<Item = T>>(i: I) -> Self {
+        let mut ret = Punctuated::new();
+        ret.extend(i);
+        ret
+    }
+}
+
+impl<T, P> Extend<T> for Punctuated<T, P>
+where
+    P: Default,
+{
+    fn extend<I: IntoIterator<Item = T>>(&mut self, i: I) {
+        for value in i {
+            self.push(value);
+        }
+    }
+}
+
+impl<T, P> FromIterator<Pair<T, P>> for Punctuated<T, P> {
+    fn from_iter<I: IntoIterator<Item = Pair<T, P>>>(i: I) -> Self {
+        let mut ret = Punctuated::new();
+        ret.extend(i);
+        ret
+    }
+}
+
+impl<T, P> Extend<Pair<T, P>> for Punctuated<T, P> {
+    fn extend<I: IntoIterator<Item = Pair<T, P>>>(&mut self, i: I) {
+        assert!(
+            self.empty_or_trailing(),
+            "Punctuated::extend: Punctuated is not empty or does not have a trailing punctuation",
+        );
+
+        let mut nomore = false;
+        for pair in i {
+            if nomore {
+                panic!("Punctuated extended with items after a Pair::End");
+            }
+            match pair {
+                Pair::Punctuated(a, b) => self.inner.push((a, b)),
+                Pair::End(a) => {
+                    self.last = Some(Box::new(a));
+                    nomore = true;
+                }
+            }
+        }
+    }
+}
+
+impl<T, P> IntoIterator for Punctuated<T, P> {
+    type Item = T;
+    type IntoIter = IntoIter<T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        let mut elements = Vec::with_capacity(self.len());
+        elements.extend(self.inner.into_iter().map(|pair| pair.0));
+        elements.extend(self.last.map(|t| *t));
+
+        IntoIter {
+            inner: elements.into_iter(),
+        }
+    }
+}
+
+impl<'a, T, P> IntoIterator for &'a Punctuated<T, P> {
+    type Item = &'a T;
+    type IntoIter = Iter<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Punctuated::iter(self)
+    }
+}
+
+impl<'a, T, P> IntoIterator for &'a mut Punctuated<T, P> {
+    type Item = &'a mut T;
+    type IntoIter = IterMut<'a, T>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        Punctuated::iter_mut(self)
+    }
+}
+
+impl<T, P> Default for Punctuated<T, P> {
+    fn default() -> Self {
+        Punctuated::new()
+    }
+}
+
+/// An iterator over borrowed pairs of type `Pair<&T, &P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Pairs<'a, T: 'a, P: 'a> {
+    inner: slice::Iter<'a, (T, P)>,
+    last: option::IntoIter<&'a T>,
+}
+
+impl<'a, T, P> Iterator for Pairs<'a, T, P> {
+    type Item = Pair<&'a T, &'a P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for Pairs<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for Pairs<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+// No Clone bound on T or P.
+impl<'a, T, P> Clone for Pairs<'a, T, P> {
+    fn clone(&self) -> Self {
+        Pairs {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+/// An iterator over mutably borrowed pairs of type `Pair<&mut T, &mut P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct PairsMut<'a, T: 'a, P: 'a> {
+    inner: slice::IterMut<'a, (T, P)>,
+    last: option::IntoIter<&'a mut T>,
+}
+
+impl<'a, T, P> Iterator for PairsMut<'a, T, P> {
+    type Item = Pair<&'a mut T, &'a mut P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PairsMut<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PairsMut<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+/// An iterator over owned pairs of type `Pair<T, P>`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IntoPairs<T, P> {
+    inner: vec::IntoIter<(T, P)>,
+    last: option::IntoIter<T>,
+}
+
+impl<T, P> Iterator for IntoPairs<T, P> {
+    type Item = Pair<T, P>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|(t, p)| Pair::Punctuated(t, p))
+            .or_else(|| self.last.next().map(Pair::End))
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<T, P> DoubleEndedIterator for IntoPairs<T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .map(Pair::End)
+            .or_else(|| self.inner.next_back().map(|(t, p)| Pair::Punctuated(t, p)))
+    }
+}
+
+impl<T, P> ExactSizeIterator for IntoPairs<T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+impl<T, P> Clone for IntoPairs<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        IntoPairs {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+/// An iterator over owned values of type `T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IntoIter<T> {
+    inner: vec::IntoIter<T>,
+}
+
+impl<T> Iterator for IntoIter<T> {
+    type Item = T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<T> DoubleEndedIterator for IntoIter<T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<T> ExactSizeIterator for IntoIter<T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<T> Clone for IntoIter<T>
+where
+    T: Clone,
+{
+    fn clone(&self) -> Self {
+        IntoIter {
+            inner: self.inner.clone(),
+        }
+    }
+}
+
+/// An iterator over borrowed values of type `&T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct Iter<'a, T: 'a> {
+    // The `Item = &'a T` needs to be specified to support rustc 1.31 and older.
+    // On modern compilers we would be able to write just IterTrait<'a, T> where
+    // Item can be inferred unambiguously from the supertrait.
+    inner: Box<NoDrop<dyn IterTrait<'a, T, Item = &'a T> + 'a>>,
+}
+
+trait IterTrait<'a, T: 'a>:
+    DoubleEndedIterator<Item = &'a T> + ExactSizeIterator<Item = &'a T>
+{
+    fn clone_box(&self) -> Box<NoDrop<dyn IterTrait<'a, T, Item = &'a T> + 'a>>;
+}
+
+struct PrivateIter<'a, T: 'a, P: 'a> {
+    inner: slice::Iter<'a, (T, P)>,
+    last: option::IntoIter<&'a T>,
+}
+
+impl<'a, T, P> TrivialDrop for PrivateIter<'a, T, P>
+where
+    slice::Iter<'a, (T, P)>: TrivialDrop,
+    option::IntoIter<&'a T>: TrivialDrop,
+{
+}
+
+#[cfg(any(feature = "full", feature = "derive"))]
+pub(crate) fn empty_punctuated_iter<'a, T>() -> Iter<'a, T> {
+    Iter {
+        inner: Box::new(NoDrop::new(iter::empty())),
+    }
+}
+
+// No Clone bound on T.
+impl<'a, T> Clone for Iter<'a, T> {
+    fn clone(&self) -> Self {
+        Iter {
+            inner: self.inner.clone_box(),
+        }
+    }
+}
+
+impl<'a, T> Iterator for Iter<'a, T> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<'a, T> ExactSizeIterator for Iter<'a, T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<'a, T, P> Iterator for PrivateIter<'a, T, P> {
+    type Item = &'a T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|pair| &pair.0)
+            .or_else(|| self.last.next())
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PrivateIter<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .or_else(|| self.inner.next_back().map(|pair| &pair.0))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PrivateIter<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+// No Clone bound on T or P.
+impl<'a, T, P> Clone for PrivateIter<'a, T, P> {
+    fn clone(&self) -> Self {
+        PrivateIter {
+            inner: self.inner.clone(),
+            last: self.last.clone(),
+        }
+    }
+}
+
+impl<'a, T, I> IterTrait<'a, T> for I
+where
+    T: 'a,
+    I: DoubleEndedIterator<Item = &'a T>
+        + ExactSizeIterator<Item = &'a T>
+        + Clone
+        + TrivialDrop
+        + 'a,
+{
+    fn clone_box(&self) -> Box<NoDrop<dyn IterTrait<'a, T, Item = &'a T> + 'a>> {
+        Box::new(NoDrop::new(self.clone()))
+    }
+}
+
+/// An iterator over mutably borrowed values of type `&mut T`.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub struct IterMut<'a, T: 'a> {
+    inner: Box<NoDrop<dyn IterMutTrait<'a, T, Item = &'a mut T> + 'a>>,
+}
+
+trait IterMutTrait<'a, T: 'a>:
+    DoubleEndedIterator<Item = &'a mut T> + ExactSizeIterator<Item = &'a mut T>
+{
+}
+
+struct PrivateIterMut<'a, T: 'a, P: 'a> {
+    inner: slice::IterMut<'a, (T, P)>,
+    last: option::IntoIter<&'a mut T>,
+}
+
+impl<'a, T, P> TrivialDrop for PrivateIterMut<'a, T, P>
+where
+    slice::IterMut<'a, (T, P)>: TrivialDrop,
+    option::IntoIter<&'a mut T>: TrivialDrop,
+{
+}
+
+#[cfg(any(feature = "full", feature = "derive"))]
+pub(crate) fn empty_punctuated_iter_mut<'a, T>() -> IterMut<'a, T> {
+    IterMut {
+        inner: Box::new(NoDrop::new(iter::empty())),
+    }
+}
+
+impl<'a, T> Iterator for IterMut<'a, T> {
+    type Item = &'a mut T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner.next()
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.inner.next_back()
+    }
+}
+
+impl<'a, T> ExactSizeIterator for IterMut<'a, T> {
+    fn len(&self) -> usize {
+        self.inner.len()
+    }
+}
+
+impl<'a, T, P> Iterator for PrivateIterMut<'a, T, P> {
+    type Item = &'a mut T;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.inner
+            .next()
+            .map(|pair| &mut pair.0)
+            .or_else(|| self.last.next())
+    }
+}
+
+impl<'a, T, P> DoubleEndedIterator for PrivateIterMut<'a, T, P> {
+    fn next_back(&mut self) -> Option<Self::Item> {
+        self.last
+            .next()
+            .or_else(|| self.inner.next_back().map(|pair| &mut pair.0))
+    }
+}
+
+impl<'a, T, P> ExactSizeIterator for PrivateIterMut<'a, T, P> {
+    fn len(&self) -> usize {
+        self.inner.len() + self.last.len()
+    }
+}
+
+impl<'a, T, I> IterMutTrait<'a, T> for I
+where
+    T: 'a,
+    I: DoubleEndedIterator<Item = &'a mut T> + ExactSizeIterator<Item = &'a mut T> + 'a,
+{
+}
+
+/// A single syntax tree node of type `T` followed by its trailing punctuation
+/// of type `P` if any.
+///
+/// Refer to the [module documentation] for details about punctuated sequences.
+///
+/// [module documentation]: self
+pub enum Pair<T, P> {
+    Punctuated(T, P),
+    End(T),
+}
+
+impl<T, P> Pair<T, P> {
+    /// Extracts the syntax tree node from this punctuated pair, discarding the
+    /// following punctuation.
+    pub fn into_value(self) -> T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Borrows the syntax tree node from this punctuated pair.
+    pub fn value(&self) -> &T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Mutably borrows the syntax tree node from this punctuated pair.
+    pub fn value_mut(&mut self) -> &mut T {
+        match self {
+            Pair::Punctuated(t, _) | Pair::End(t) => t,
+        }
+    }
+
+    /// Borrows the punctuation from this punctuated pair, unless this pair is
+    /// the final one and there is no trailing punctuation.
+    pub fn punct(&self) -> Option<&P> {
+        match self {
+            Pair::Punctuated(_, p) => Some(p),
+            Pair::End(_) => None,
+        }
+    }
+
+    /// Mutably borrows the punctuation from this punctuated pair, unless the
+    /// pair is the final one and there is no trailing punctuation.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use proc_macro2::Span;
+    /// # use syn::punctuated::Punctuated;
+    /// # use syn::{parse_quote, Token, TypeParamBound};
+    /// #
+    /// # let mut punctuated = Punctuated::<TypeParamBound, Token![+]>::new();
+    /// # let span = Span::call_site();
+    /// #
+    /// punctuated.insert(0, parse_quote!('lifetime));
+    /// if let Some(punct) = punctuated.pairs_mut().next().unwrap().punct_mut() {
+    ///     punct.span = span;
+    /// }
+    /// ```
+    pub fn punct_mut(&mut self) -> Option<&mut P> {
+        match self {
+            Pair::Punctuated(_, p) => Some(p),
+            Pair::End(_) => None,
+        }
+    }
+
+    /// Creates a punctuated pair out of a syntax tree node and an optional
+    /// following punctuation.
+    pub fn new(t: T, p: Option<P>) -> Self {
+        match p {
+            Some(p) => Pair::Punctuated(t, p),
+            None => Pair::End(t),
+        }
+    }
+
+    /// Produces this punctuated pair as a tuple of syntax tree node and
+    /// optional following punctuation.
+    pub fn into_tuple(self) -> (T, Option<P>) {
+        match self {
+            Pair::Punctuated(t, p) => (t, Some(p)),
+            Pair::End(t) => (t, None),
+        }
+    }
+}
+
+#[cfg(feature = "clone-impls")]
+#[cfg_attr(doc_cfg, doc(cfg(feature = "clone-impls")))]
+impl<T, P> Clone for Pair<T, P>
+where
+    T: Clone,
+    P: Clone,
+{
+    fn clone(&self) -> Self {
+        match self {
+            Pair::Punctuated(t, p) => Pair::Punctuated(t.clone(), p.clone()),
+            Pair::End(t) => Pair::End(t.clone()),
+        }
+    }
+}
+
+impl<T, P> Index<usize> for Punctuated<T, P> {
+    type Output = T;
+
+    fn index(&self, index: usize) -> &Self::Output {
+        if index == self.len() - 1 {
+            match &self.last {
+                Some(t) => t,
+                None => &self.inner[index].0,
+            }
+        } else {
+            &self.inner[index].0
+        }
+    }
+}
+
+impl<T, P> IndexMut<usize> for Punctuated<T, P> {
+    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
+        if index == self.len() - 1 {
+            match &mut self.last {
+                Some(t) => t,
+                None => &mut self.inner[index].0,
+            }
+        } else {
+            &mut self.inner[index].0
+        }
+    }
+}
+
+#[cfg(feature = "printing")]
+mod printing {
+    use super::*;
+    use proc_macro2::TokenStream;
+    use quote::{ToTokens, TokenStreamExt};
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl<T, P> ToTokens for Punctuated<T, P>
+    where
+        T: ToTokens,
+        P: ToTokens,
+    {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            tokens.append_all(self.pairs());
+        }
+    }
+
+    #[cfg_attr(doc_cfg, doc(cfg(feature = "printing")))]
+    impl<T, P> ToTokens for Pair<T, P>
+    where
+        T: ToTokens,
+        P: ToTokens,
+    {
+        fn to_tokens(&self, tokens: &mut TokenStream) {
+            match self {
+                Pair::Punctuated(a, b) => {
+                    a.to_tokens(tokens);
+                    b.to_tokens(tokens);
+                }
+                Pair::End(a) => a.to_tokens(tokens),
+            }
+        }
+    }
+}